1. Field of the Invention
This invention relates generally to the field of water purification, and more specifically to an apparatus and process for recovering metals from aqueous solutions by passing an aqueous solution, which contains dissolved metals (e.g., gold, silver, iron, aluminum, platinum, uranium, etc.) through a very high voltage electric field accompanied by a very small trickle current charge to enhance adsorption, polarization, ion exchange or otherwise agglomerate the metal and then, filtering, adsorbing, exchanging or otherwise separating the metal from the water.
2. State of the Prior Art
The removal of impurities and contaminants, including dissolved metals, from water has long been an important issue due to both environmental and public health concerns, and there are industrial interests in processes for capturing and recovering dissolved metals from aqueous solutions. Many devices and processes have thus been designed to treat contaminated water in order to make it safe for consumption or other public use. Metals of all types (e.g., gold, silver, iron, aluminum, platinum, uranium, selenium, and arsenic etc.) dissolved or suspended in water comprise one such category of impurities, and commonly end up in the effluent wastewater of mining, city water discharge or other industrial operations including, most recently, from the semiconductor industry, as well as from many other industrial processes, commercial products, and natural sources, such as soils and groundwater aquifers. There are many known processes for removing metals from an aqueous solution. For example, electrodeposition processes, in which suspended or dissolved metals in an electrolyte are deposited onto an electrode by electrolysis are common. However, these known electrodeposition processes become very inefficient and cease to be cost effective when applied to aqueous solutions containing low concentrations of metals, which is often the case, especially in environmental clean-up and water purification applications. There are other processes for removing metals from aqueous solutions, such as chemical reactions to precipitate compounds, use of flocculents, adhesion to activated carbons and other materials, and the like, but such processes are also expensive, require substantial quality controls, and have their own recovery and disposal problems.
Accordingly, a general object of this invention is to provide a more economical process and apparatus for removing or recovering metals from aqueous solutions, particularly those aqueous solutions having low concentrations of the metals.
A more specific object of this invention is to treat an aqueous solution comprising dissolved and/or suspended metals in a manner that enhances removal of the metals by filtration and/or adsorption.
It is also an object of this invention to provide a process and apparatus for more efficiently removing or recovering metals from aqueous solutions.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as embodied and broadly described herein, the method of this invention may involve passing an aqueous solution, which contains dissolved or suspended metals (e.g., gold, silver, iron, aluminum, platinum, uranium, etc.) through a very high voltage electric field accompanied by a very small trickle current charge. The high voltage electric field in combination with the trickle current alters the characteristics of the dissolved metalsxe2x80x94possibly causing the metal ions or atoms to polarize, adsorb, agglomerate, or otherwise group togetherxe2x80x94so that they will be more susceptible to being captured and retained by adsorption or ion exchange on a mechanical trapping by a filter medium.
The process of the present invention is not electrolytic deposition, i.e., it is not an electrolytic process in which metal ions in the aqueous solution carry an electric current between an anode and a cathode and are deposited on the cathode. On the contrary, the metal ions in this invention do not carry a current and do not deposit on either of the high voltage electrodes. Instead, as explained above, the metal is collected by ion exchange or adsorption on, or a mechanical removal by, one or more filter media downstream from the electrodes. Therefore, the high voltage field, assisted by a small trickle current, causes the metal ions in the aqueous solution to come out of solution, possibly by forming into suspended solids in the water, or to undergo some other positive ion change that makes them more susceptible to adsorption or other filtering, which can be removed by conventional, non-electrical, filtration. Unlike electrolysis, one of the pair of high voltage electrodes used in this invention is insulated, so there is virtually no current flow in the process, except for the small trickle current as will be explained below, so electric power consumption is very lowxe2x80x94making this process very economical for recovery of metals from aqueous solutions.
The apparatus of this invention may include an inner electrode deposed within an outer electrode which may be a grounded stainless steel tube, contained within a plastic tube through which metal-bearing water is passed. A high voltage electric field is established between the two electrodes and the metal-bearing water passes between the electrodes and through the high voltage electric field. A trickle current is applied directly to the water within the electric field. One of the electrodes may be electrically insulated and sealed from the water to minimize the electrical current flowing through the treatment chamber and to prevent electroplating. After flowing past the electrodes and the electric field, the water flows through at least one filter and optionally through a holding tank containing a buffering solution. Dissolved or suspended metals are extracted from the water and are collected on the various filters selected specifically to attract a certain metal or group of metals. These collected metals may then be disposed of or reused.